1. Field of the Invention
The present invention relates to an water-free, electrorheological fluid capable of controlling the viscosity by application of an electric field.
2. Prior Art
An electrorheological fluid is a suspension comprising an electrically insulating liquid and inorganic or polymeric particles dispersed therein, whose viscosity is rapidly and reversibly changed by applying an electric field to the fluid, for example, from a liquid state to a plastic state or a solid state and vice versa. This phenomenon is called Winslows' effect.
Generally, particles whose surfaces can be readily polarized by application of an electric field are used as dispersible particles. As inorganic dispersible particles, silica is disclosed in U.S. Pat. No. 3,047,507; British Patent No. 1,076,754; and Japanese Patent Application Kokai (Laid-open) No. 61-44998, and zeolite is disclosed in Japanese Patent Application Kokai (Laid-open) No. 62-95397. As polymeric dispersible particles, alginic acid, carboxyl-containing glucose and sulfone-containing glucose are disclosed in Japanese Patent Application Kokai (Laid-open) No. 51-33783; divinylbenzene-cross-linked polyacrylic acid is disclosed in Japanese Patent Application Kokai (Laid-open) No. 53-93186; and resol-type phenol resin is disclosed in Japanese Patent Application Kokai (Laid-open) No. 58-179259.
Mineral oil, silicone oil, fluorocarbon oil, halogenated oil, etc. are known as an electrically insulating oil.
In the above-mentioned prior art it is necessary that water is adsorbed on the surfaces of dispersed particles to enhance the electrorheological effect, and thus a small amount of water is contained in the electrorheological fluid.
Mechanism of increasing the viscosity of an electrorheological fluid by application of an electric field thereto can be clarified according to the electrical double layer theory. That is, an electrical double layer is formed on the surfaces each of dispersed particles in an electrorheological fluid, and when no electric field is applied to the electrorheological fluid, the particles are repelled from one another on their surfaces and are never brought into an alignment of dispersed particles. When an electric field is applied thereto, an electrical deviation takes place on the electrical double layers of the dispersed particles, and the dispersed particles are aligned by an electrostatic attractive force to form a bridge of dispersed particles. Thus, the viscosity of the fluid is increased, sometimes resulting in solidification. The water contained in the electrorheological fluid promotes to form the electrical double layers.
The electrorheological fluid is expected to be used in engine mounts, shock absorbers, clutch, etc.
In the prior art, the presence of water is required for obtaining a satisfactory electrorheological effect, and thus there are still some problems due to the presence of water. One of the problems is a short circuit due to the easy current passage at an elevated voltage. Another problem is a limited applicable temperature range due to the reduced electrorheological effect by solidification of water into ice at 0.degree. C. or lower, or by evaporation of water at 100.degree. C. or higher. These problems have been main factors of preventing practical application of the electrorheological fluid.
A water-free electrorheological fluid based on fine carbon particles is disclosed in Japanese Patent Application Kokai (Laid-open) 3-47896, but has a low electrorheological effect, because the fine carbon particles so far used is only the heat-treated one.